In 1997 he appears to be in charge of Medical (Dragon's Domain) but by 1999 he is Dr Helena Russell's deputy. Alternatively the more senior medical chief in 1997 may not have been present when the Ultra Probe was brought in; or the chief was a scientific appointment who would not be involved in treatment. In any case, Mathias does not seem to resent Helena. He is devoted to his job and his patients.

In the Powys novels, Mathias is dissected by Lucas in Resurrection, and Helena has to bargain with Balor to revive him. In Omega it is revealed he was an army medic in combat. Helena finds his dead body after the battle in Alpha

"Frank Warren died at thirteen twenty eight." (Breakaway)
"Something strange, Doctor. Could you come to the Care Unit straight away?" (Matter Of Life And Death)
"You'll never beat me, you know." (Black Sun)
"You have a lovely optic nerve, Dr Russell." (Ring Around The Moon)
"I can't control everything! I am not a computer!" (Guardian Of Piri)
"It's incredible he's alive at all." Koenig:"But he'll survive?" Mathias: "Oh yes. On courage." (Dragon's Domain)
"Morrow! What's happened to the power in here!" "But our patients are dying!" (Force Of Life)
"Morrow! What the hell's going on? If you don't give me more heat you might as well shoot my patients!" (The Testament Of Arkadia)
"Spacesuits, Commander. The atmosphere is thinning fast." (The Last Sunset)
"But, Professor, he had caps on his teeth." (The Full Circle)
"Hurry! It won't hold!" (War Games)
"Don't look so worried. He'll be alright. He'll regain consciousness in an hour." (The Exiles)

Helena tells off Mathias when Graham dies in Medical. He prepares for Kano's link to computer. Later at the party in Medical, he is doing magic tricks. When Koenig wakes up, he offers him medicine, then drinks it himself.

Mathias doesn't seem to have been at the birth, but he does help diagnose Jackie's deafness. He witnesses the transformation to Jarak, and Helena is forced to strangle him. He gasps for breath in Medical. After Jarak and Rena seal themselves in Medical, he is seen with his head in his hands.